1. Field of the Invention
The present invention generally relates to shielding devices for minimizing electromagnetic interference and, more particularly, is concerned with an enclosure and an assembly employing the enclosure and opposing covers interfitted with releasable attachment means defined on opposite upper and lower portions of the enclosure which provide for effective shielding of circuit board components against electromagnetic interference.
2. Description of the Prior Art
Electronic components found in various types of transmitters, receivers, computers and other electronic devices emit or are susceptible to electromagnetic radiation. It is therefore desirable to shield circuit components to reduce undesirable electromagnetic interference (EMI) and/or susceptibility effects with the use of conductive shields that reflect or dissipate electromagnetic charges and fields. Such shields are generally grounded to allow electrical charges and fields to be dissipated without disrupting the operation of the electronic components enclosed within the shield.
Various types of shielding devices for electronic components mounted on printed circuit boards have been proposed in the prior art. Representative examples of such shielding devices are those disclosed in U.S. Pat. No. 4,754,101 to Stickney et al., U.S. Pat. No. 4,841,414 to Hibino et al., U.S. Pat. No. 5,014,160 to McCoy, Jr., U.S. Pat. No. 5,043,848 to Rogers et al., U.S. Pat. No. 5,095,177 to Johnson, U.S. Pat. No. 5,160,807 to Fry et al., U.S. Pat. No. 5,175,395 to Moore, U.S. Pat. No. 5,354,951 to Lange, Sr. et al., Japan Pat. No. 62,595 to Tsunoda and German Pat. No. 3,736,833 to Bardon. These shielding devices frequently include a base frame which is mounted to a printed circuit board and surrounds circuit board components and a cover which fits over and connects with the base frame and encloses the printed circuit board components.
Various difficulties may be encountered with respect to providing a satisfactory connection of the cover to the base frame. The connection must secure the cover to the base frame in a reliable manner which prevents dislodgement due to shock and vibration. At the same time, the connection must permit easy removal of the cover for periodic visual inspection of the components enclosed by the shield.
The one shielding assembly disclosed in U.S. Pat. No. 5,354,951 to Lange, Sr. et al., and assigned to the assignee of the present invention, has a connection configuration which has been found to be highly satisfactory in releasably securing a top cover to an enclosure of the shielding assembly. The enclosure of the shielding assembly of this patent includes a plurality of interconnected walls for surrounding an electronic component on a circuit board, a plurality of mounting pins attached to lower portions of the walls for attachment to the circuit board, and a plurality of outer and inner tabs formed in upper portions of the walls for releasably mounting the top cover thereto. The tabs are disposed in a spaced, alternating and offset relationship to one another along the upper portions of the walls so as to create an annular channel between the outer and inner tabs extending along the upper portions of the walls. The top cover has side portions which are removably insertable into the annular channel of the upper portions of the walls of the assembly and into a frictional fitting relation therewith to thereby removably mount the top cover over the enclosure and provide an effective electromagnetic interference shield for the electronic component.
It has been perceived by the inventors herein that a continuing need still exists for improvements in the design of shielding devices for circuit board components that will adapt such devices for use in other applications.